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M4A87TD/USB3 motherboard, AMD Phenom 2 CPU, 8 gig ddr3, Zotac Gtx660 2 gig graphics, Point ATX 12V 750W PSU, Onboard sound, lan etc,

I had a random complete system shutdown with no warning. I initially thought it was a overheating problem as I had just put my case sides back on. There was no smell or associated crakeling noise. After letting it cool down I tried to restart with no response when the power switch was pressed. I left it overnight and tried again in the morning again with no response. The standby green LED is lit, the red core unlocking switch LED is lit and the MEMOK button when pressed flashes once. The board will not power up, the fans don't move or twitch or move and of course there are no POST beeps.

I have tried resetting the bios, tried a new bios battery. I have also tried stripping it down to basic components, trying single sticks of memory in different slots. Double checked the front panel connections, even bridging the power switch posts, again with no response. I then stripped everything out of the case placing all on cardboard and repeated all the diagnostics above. I have also tried different power cables.

I don't understand what has happened if the PSU and Motherboard are dead how are the LED's lit? Could it be the CPU or the Graphics Card? Is there anything I have missed or something else I can try to find out what's is wrong. At this point I'm tearing my hair out and I haven't got much of that left, so any help will be gratefully received.

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  • Techie007 I searched further and found the "paper clip" test. I tried it and it has proven, up to now that the PSU or at least part of it has died coupled with the knowledge you supplied about the multiple circuits has been really useful. I'm going to double check with a friends multi meter. But very helpful.
    – Stuart Brownbridge
    Commented Dec 19, 2015 at 0:00

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Remove everything except the CPU, PSU and motherboard. If you still get no POST Beeps (telling you there's no RAM, or no GPU), then you know its a bad PSU, bad motherboard or bad CPU.

  • Try a different (known-good) PSU.
  • If that doesn't help, try a replacement motherboard.
  • If that doesn't help, try a different (known-good) CPU.

I don't understand what has happened if the PSU and Motherboard are dead how are the LED's lit

The PSU and motherboard use multiple power lines, and are complex devices with multiple circuits. So just because one/some circuits are still working (enough to light LEDs anyway), it doesn't mean all others are functioning fully.

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